1. Field of the Invention
The present invention relates generally to pollution control, and more specifically to collection and treatment of solid pollutants which collect on the surface of streets.
2. Description of Related Art
Significant efforts and resources are being expended to identify and control various sources and types of pollution. Pollutants emitted from automobiles are among the most notorious and visible, and therefore have been the subject of extensive abatement efforts for more than 25 years. The primary focus in controlling automobile emissions however has been on controlling airborne pollutants such as unbumed hydrocarbons, carbon monoxide, NO.sub.x, and sulfur containing compounds. Another significant, yet largely unrecognized form of pollution by automobiles occurs in the form of small particulates which collect on the surface of streets. Some of these particulate pollutants originate as solid or liquid combustion products which settle or condense on the street surface. Others are generated by the normal wear of frictional mechanisms such as brakes and clutches, or by the normal wear of tires and auxiliary drive belts fitted to most automobiles.
These particulate pollutants as a group contain numerous substances, some of which may be water-soluble, which are problematic if allowed to accumulate, including polynuclear aromatic hydrocarbons, oils, greases, rubber particles, solid carbonaceous combustion products, and metals such as copper, lead and zinc. If left to accumulate on the street surface, some of these pollutants are continually disturbed by vehicles using the streets and circulated in the form of airbome dust. If left to be finally carried off by the natural action of rain, the pollutants may end up on local bodies of water, which may themselves be the subject of extensive anti-pollution efforts.
The problem can be particularly acute in areas which experienced periods of little or no rainfall. The shortage of rainfall impacts this problem in more ways than one. First, if there is an extended period without rainfall, the pollutants will continue to accumulate on the street surfaces during that period. Secondly, it is often during these times of low rainfall that local bodies of water experience low flows, or reduced volumes. When rain does finally fall, a relatively large amount of solid pollutants which have been accumulated are then suddenly discharged into a relatively low volume of water, resulting in relatively high pollutant concentrations.
Up until now there has been very little effort devoted to control of these solid street surface pollutants, and no satisfactory solution to their removal and control has been found. Normal street sweeping is used to remove debris and larger particles. Sweepers may be equipped with vacuum cleaning equipment, but such equipment has not been shown to be effective at removing small particulate pollutants from the surface of the street. As a result, these pollutants normally end up being discharged untreated with storm water runoff. This is particularly true in areas where the storm sewer system is separate from the sanitary sewer system. In these instances, pollution treatment facilities are normally provided only on the sanitary sewer system, with no provision made for treatment of the storm sewer discharge. There is minimal treatment of collected street surface runoff in some cases, but mostly in the form of swirl concentrators or similar devices. Swirl concentrators typically remove 10-30% of the suspended solids, but are ineffective at removing extremely small particles and dissolved pollutants.
Efforts at education raise awareness of the problem, and may serve to reduce vehicle usage overall, but have no effect on controlling whatever quantity of pollutants which find their way to the street surface.
A need therefore remains for a method of collecting and treating small particulate pollutants from street surfaces which otherwise go untreated.